Generally speaking, a conventional network device applied to a high speed network such as 40 GHz Ethernet or 100 GHz Ethernet is arranged to generate a plurality of packets to the high speed network and to generate idle data between two consecutive packets. The number of idle data such as idle bytes to be generated between packets is preliminary configured, and the number configured is smaller than the number of total bytes generated by the conventional network device at each cycle. Thus, it is possible for the conventional network device to generate end of packet for this current packet and start of packet for the next packet at the same cycle. It is very difficult to implement or design the packet generation scheme for the conventional network device. In addition, the design for fixed number of idle bytes between each two packets may be impractical.